Transdermal devices have been widely prescribed for decades in the treatment of is systemic diseases and local conditions. During passive transdermal delivery, an active agent is delivered into a mammal by using a concentration gradient across a barrier membrane (e.g., through passive diffusion through skin). For example, a patch containing the drug in high concentration is affixed to the skin of a patient.
Electricity may be employed to facilitate drug transport across the skin barrier. In electricity-assisted devices, an electric potential (voltage) is applied to the membrane to facilitate drug transport. In transdermal iontophoresis, an ionized drug migrates into the skin driven by an applied electric potential gradient. Anionic drugs are delivered into the skin under the cathode (negatively charged electrode), while cationic drugs are delivered under the anode (positively charged electrode). Iontophoresis enables enhanced as well as better control of permeation rate of the ionic species into the skin.
The most common design of an iontophoresis device includes a power source (e.g., a battery), an electric control mechanism, and two separate conductive electrodes. Each conductive electrode is in contact with a separate electrolyte composition (with or without an active agent). The electrolyte or ionic active composition is generally either an aqueous solution contained in a liquid chamber or a semi-solid. The assembly of the conductive electrode and electrolyte composition is often referred to as “an electrode assembly” or simply “an electrode.” The two electrode assemblies are usually affixed to the skin separated by electric insulation between them.
Alternatively, the two electrode assemblies may be constructed into a single iontophoresis device with an electric insulating material built between the two electrode assemblies for electrical isolation to prevent shorting current. An example of such an iontophoresis device is disclosed in U.S. Pat. No. 5,387,189.
In another variation of the common iontophoresis device designs, the electrolyte composition in one of the two electrode assemblies is eliminated, and the conductive electrode is placed directly in contact with the skin to complete the electric circuit. An example of such iontophoresis device is disclosed in U.S. Pat. No. 6,385,487.
During a typical iontophoresis operation (mono-polar operation), one of the two electrodes (i.e., active electrode) drives the active agent into the skin. The other electrode (i.e., disperse electrode) serves to close the electrical circuit through the skin. Sometimes, a second active agent of opposite electric charge can be placed into electrolyte composition in contact with the second electrode, thus, being delivered into the skin under the second electrode. Alternatively, the electric polarity of the first and second electrodes can be reversed periodically to drive ionic species under both electrodes (bi-polar operation). A bi-polar iontophoresis device for transdermal drug delivery is disclosed U.S. Pat. No. 4,406,658.
Using a galvanic couple as the power source in iontophoresis device is well known in the art. See e.g., U.S. Pat. Nos. 5,147,297, 5,162,043, 5,298,017, 5,326,341, 5,405,317, 5,685,837, 6,584,349, 6,421,561 and 6,653,014. Typical materials from which a galvanic couple is made includes a zinc donor electrode and a silver chloride counter electrode. Such a combination produces an electric potential of about one volt. Such a galvanic couple powered iontophoresis system, absent some controlling means, activates automatically when body tissue and/or fluids form a complete circuit with the system to generate the electricity.